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Phosphorosaurus (halisaurine mosasaur), new species from Japan (free pdf)

Ben Creisler

A new paper in open access:

Takuya Konishi, Michael W. Caldwell, Tomohiro Nishimura, Kazuhiko
Sakurai & Kyo Tanoue (2015)
A new halisaurine mosasaur (Squamata: Halisaurinae) from Japan: the
first record in the western Pacific realm and the first documented
insights into binocular vision in mosasaurs.
Journal of Systematic Palaeontology (advance online publication)

A specimen of a halisaurine mosasaur is reported from Japan for the
first time, closing the pre-existing biogeographical gap between the
Middle East and the eastern Pacific. Phosphorosaurus ponpetelegans sp.
nov., from the lowermost Maastrichtian of Hokkaido, has been assigned
to the genus Phosphorosaurus for sharing the following suite of major
cranial characters with P. ortliebi, the type species from Belgium:
apex of posterodorsal triangular plateau on frontal reaching level of
interorbital constriction; frontal lateral border forming a step-like
junction between interorbital and preorbital segments of frontal;
preorbital segment of frontal sloping anteroventrally; and stapedial
meatus parallel-sided in latero-medial view. Potential autapomorphies
that distinguish P. ponpetelegans from other members of Halisaurinae
include: postorbitofrontal jugal process elongate and stalk-like,
projecting laterally; this process distally bearing a ventrally facing
depression for jugal articulation; and lateral surangular–articular
suture angular rather than round. The long and laterally projecting
jugal processes, when combined with a depressed as well as narrow
snout, provide compelling evidence for well-developed binocular vision
for the new mosasaur, with an estimated binocular field of view (BFoV)
of 35°. This value is unusually high for non-ophidian squamates that
typically exhibit a BFoV of 10—20°, and is higher than those of other
measured mosasaur taxa by at least 5°. Among colubrid snakes,
nocturnal species exhibit greater BFoV than diurnal ones in both
arboreal and terrestrial taxa. Known also from the Maastrichtian of
Hokkaido are fossils of lantern fish (myctophids) and 10-armed
cephalopods (coleoids), both of which are typically bioluminescent
today. It is hence proposed that the exceptionally large,
forward-facing eyes of P. ponpetelegans may well have been a special
adaptation for a nocturnal lifestyle, where they hunted small,
bioluminescent prey at night while avoiding direct competition with
larger, more piscine mosasaurine taxa such as Mosasaurus hobetsuensis
that co-existed with P. ponpetelegans.